An emerging category of electronic devices is time-of-flight (TOF) systems. The TOF systems find applications in accelerometers, monolithic gyroscopes, light sensors, conveyor belts, depth sensing, proximity sensing, gesture recognition and imagers. A TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses. The target is any object of interest which may include, but not limited to, a human, an automated component, an animal, an electronic device etc. A TOF sensor in the TOF system receives the reflected light pulses. The TOF sensor receives the reflected light pulses after a time-of-flight, which is proportional to a distance of the target from the TOF system.
The TOF sensor includes a pixel array having a plurality of pixels. The pixel array receives the reflected light pulses. The pixel array collects light for a predetermined amount of time after the emission of the light by the light source. Light reflected from a far away object travels a longer distance and therefore has a longer time-of-flight, whereas light reflected from a nearby object is received after short time-of-flight. Each pixel in the pixel array generates two outputs. These two outputs are not purely differential. A common mode signal obtained from these two outputs provides information about a level of ambient light. A differential signal obtained from these two outputs provides information about a depth of the target.
Both common mode signal and differential signal are converted to digital signals using analog to digital converters (ADCs). As resolution requirement increases, a power required to drive an ADC increases proportionately, and an area required by the ADC also increases proportionately. Thus, the ADCs take a significant area of a TOF system. Also, when multiple ADCs are used in the TOF system, a large power is required to drive these ADCs.